Method, system and program product for boundary i/o testing employing a logic built-in self-test of an integrated circuit

ABSTRACT

A testing method is provided which includes verifying at least one external signal path of an electronic package environment by testing an input/output (I/O) circuit of an integrated circuit of the electronic package environment with a logic built-in self-test (LBIST) of the integrated circuit, wherein the external signal path being verified is electrically coupled to the tested I/O circuit. A result of verifying of the at least one external signal path is manifested in the integrated circuit&#39;s signature, which characterizes a response of the I/O circuit to the LBIST. In another aspect, the verifying of the at least one external signal path includes concurrently testing another I/O circuit of another integrated circuit, which is also electrically coupled to the external signal path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 10/981,225, filed Nov. 4, 2004, and published on May 4, 2006 asU.S. Patent Publication No. 2006/0095820 A1, entitled “Method, System,and Program Product for Boundary I/O Testing Employing a Logic Built-InSelf-Test of an Integrated Circuit”, by Rich et al., the entirety ofwhich is hereby incorporated herein by reference. Further, thisapplication contains subject matter which is related to the subjectmatter of U.S. patent application Ser. No. 10/980,938, filed Nov. 4,2004, and published May 18, 2006 as U.S. Patent Publication No. US2006/0107149 A1, entitled “Method, System, and Program Product forControlling Test Data of a Logic Built-In Self-Test of an IntegratedCircuit”, by Rich et al., which is assigned to the same assignee as thisapplication, and which is hereby incorporated herein by reference in itsentirety.

TECHNICAL FIELD

This invention relates in general to testing integrated circuits and,more particularly, to a technique for boundary input/output testing ofan integrated circuit within a logic built-in self-test of theintegrated circuit.

BACKGROUND OF THE INVENTION

With the increased complexity and density of today's high-endapplication-specific integrated circuit (ASIC) chips and higher-levelelectronic packages, there is a corresponding increase in the timerequired to verify the functionality of these complex packagecombinations. Typically, multiple independent logic built-in self-test(LBIST) runs are needed to verify the internal logic of multiple chipsof an electronic package. If the electronic package has arrays, multiplearray built-in self-test (ABIST) runs may also be executed as a separatestep. In order to guarantee predictability for LBIST tests, the inputsto each chip are conventionally inhibited at the boundary logic.Subsequently, a second set of tests is performed to check input/output(I/O) connections at chip boundaries (e.g., reference IEEE Std 1149.1Boundary Scan). These tests are typically DC-type tests, which verifythat each I/O connection does not have a stuck fault, i.e., the I/Oconnection is not stuck at logic-level 0 or 1.

In order to perform the boundary scan tests, detailed information isrequired about the interconnections of each chip in the electronicpackage environment. For example, each I/O source, I/O sink, and I/Oenable control path must be identified for boundary scan initializationand validation. Since the test topology set-up is typically remotelyperformed, with scan operations being transported to the hardwarethrough a serial service processor interface such as JTAG, there isadditional overhead introduced by performing these tests. Therefore,there exists a need in the art to further facilitate performing boundaryscan checks, and there is a need to reduce the complexity of maintainingI/O connection information for multiple-chip electronic packageconfigurations on a service processor. There is also a need to provideI/O boundary checking capability on less sophisticated hardwareplatforms that do not have service processor attachments.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and additional advantagesare provided through the provision of a method of testing an externalsignal path of an electronic package environment. In one aspect, themethod includes verifying at least one external signal path of theelectronic package environment by testing an input/output (I/O) circuitof the integrated circuit with a logic built-in self-test (LBIST) of theintegrated circuit. The at least one external signal path being verifiedis electrically coupled to the tested I/O circuit. A result of theverifying of the at least one external signal path is manifested in theintegrated circuit's signature, which characterizes a response of theI/O circuit to the LBIST.

In other aspects, the method includes concurrently testing the I/Ocircuit and one or more other circuits of the integrated circuit.Further, the verifying of at least one external signal path can includeconcurrently testing at least another I/O circuit, which is electricallycoupled to the at least one external signal path, of at least anotherintegrated circuit of the electronic package environment with at leastanother LBIST. In yet another aspect, a test input for the I/O circuitis selected from an external input to the integrated circuit on the atleast one external signal path or a test pattern generated by the LBISTof the integrated circuit.

Systems and computer program products corresponding to theabove-summarized methods are also described and claimed herein.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 illustrates one partial embodiment of an integrated circuit witha logic built-in self-test and integrated boundary input/output testing,in accordance with an aspect of the present invention;

FIG. 2 illustrates a flow diagram of one embodiment of a logic built-inself-test with integrated testing of input/output circuits, inaccordance with an aspect of the present invention;

FIG. 3 illustrates one embodiment of deterministic boundary test-patterngenerator logic of FIG. 1 together with one embodiment of a boundaryscan driver channel of FIG. 1, in accordance with an aspect of thepresent invention;

FIG. 4 illustrates one embodiment of driver-boundary-latch enable-signallogic for an electronic package environment having multiple packagelevels, in accordance with an aspect of the present invention;

FIG. 5 illustrates an example of an electronic package environment inwhich integrated circuits perform logic built-in self-tests withintegrated input/output testing, in accordance with an aspect of thepresent invention;

FIG. 6 illustrates identification register settings for two exemplarytest configurations of integrated circuits in the electronic packageenvironment of FIG. 5, in accordance with an aspect of the presentinvention;

FIG. 7 illustrates one embodiment of a boundary receiver latch module ofa boundary scan receiver channel of FIG. 1, in accordance with an aspectof the present invention;

FIG. 8 illustrates one embodiment of a test input selection signalgenerator for the input/output groups of an electronic packageenvironment, in accordance with an aspect of the present invention;

FIG. 9 illustrates one embodiment of a boundary driver latch module of aboundary scan receiver channel of FIG. 1, in accordance with an aspectof the present invention; and

FIG. 10 illustrates one embodiment of a boundary driver latch module fora bidirectional bus, in accordance with an aspect of the presentinvention.

BEST MODE FOR CARRING OUT THE INVENTION

Generally stated, in one aspect, presented herein is the verification ofinput/output circuits of an integrated circuit being integrated within alogic built-in self-test (LBIST) of the integrated circuit. Suchverification of input/output circuits is provided by enabling theinput/output (I/O) circuits at the boundary scan latches so that I/Odata to other chips is received by those other chips, which areconcurrently conducting logic built-in self-tests, and that output datasent by those other chips is received by the integrated circuit. Inother words, the verification of I/O circuits is integrated within LBISTtesting by configuring the I/O circuits of chips involved in the test tobe concurrently uninhibited, rather than inhibiting I/O circuits at theboundary logic of each chip during self-test as is the conventionalapproach.

FIG. 1 illustrates one embodiment of a logic built-in self-testcircuitry with integrated boundary input/output testing, in accordancewith an aspect of the present invention. Logic built-in self-testcircuit 100 includes pseudo-random test pattern generator (PRPG) 110,scan channels 130 a, 130 b, and 130 c, boundary scan receiver channel132, boundary test pattern generator 120, boundary scan driver channel134, multiple-input signature register (MISR) 140, self-test statemachine (STSM) 150, and on-product clock generators (OPCG) 160 a through160 n.

Each scan channel 130 a, 130 b, 130 c and boundary scan receiver channel132 is driven with a pseudo-random test pattern from pseudo-randomtest-pattern generator 110 during the scan initialization phase of anLBIST iteration. Boundary scan receiver channel 132 can select externalinput 133 to provide test data for an input circuit of the integratedcircuit. Alternatively, boundary scan receiver channel 132 can selectinternal input 136 to provide test data from boundary test patterngenerator 120. Each instance of a boundary scan receiver channel selectsan external input or an internal input from boundary test patterngenerator 120 based on an integrated circuit's particular requirements.In one implementation, boundary scan driver channel 134 is driven by adeterministic test pattern generated by boundary test pattern generator120, and boundary scan driver channel 134 drives output line 135 of theintegrated circuit. Each scan channel 130 a, 130 b, 130 c drives aninternal logic circuit (not shown in FIG. 1) of the integrated circuitto provide input test data for the internal logic circuits of theintegrated circuit. As described in more detail hereinbelow, scanchannels 130 a, 130 b, 130 c, boundary scan receiver channel 132, andboundary scan driver channel 134 also capture LBIST input test data. Theinput test data captured by scan channels 130 a, 130 b, 130 c, boundaryscan receiver channel 132, and boundary scan driver channel 134 areprovided to multiple-input signature register 140, which compares theactual response of the integrated circuit to the LBIST to the signatureof a properly functioning integrated circuit.

Boundary scan receiver channel 132 of FIG. 1 comprises a receiverboundary latch in accordance with an aspect of the present invention,and boundary scan driver channel 134 comprises a driver boundary latchin accordance with an aspect of the present invention. One embodiment ofa receiver boundary latch of boundary scan receiver channel 132 isillustrated in FIG. 7. FIGS. 9 and 10 illustrate exemplary embodimentsof a driver boundary latch of boundary scan driver channel 134. Randompatterns are input to the receiver boundary latches to apply randomstimuli to internal logic circuits of the integrated circuit, whereas adeterministic pattern is used to prime the driver boundary latches toassure that the integrated circuit has a predictable signature whetherthe integrated circuit's I/O circuits are inhibited or not. Thisconfiguration assures that the states of the boundary I/O circuits whichinfluence internal logic circuits' states are also compressed into theLBIST signature. Consequently, an LBIST signature is produced whichreflects the condition of the I/O connections as well as the internalchip logic when I/O circuits are uninhibited. Therefore, a misconnectedor stuck-fault I/O circuit will cause a signature mismatch in the samefashion as an internal logic fault.

The embodiment of a logic built-in self test to test input/outputcircuits of an integrated circuit illustrated in FIG. 1 may include morethan one boundary scan receiver channel and more than one boundary scandriver channel providing inputs to the MISR.

The integration of I/O circuit verification with logic built-inself-test of internal logic circuits requires additional functionalityin the LBIST iteration sequence. FIG. 2 illustrates a flow diagram 200of one embodiment of a logic built-in self-test with integrated testingof input/output circuits, in accordance with an aspect of the presentinvention. The process begins with the integrated circuit entering aself-test mode 210. Then, the boundary latches are set up to acceptinput from the scan paths of the logic built-in self-test forinitialization purposes 220. The processing proceeds with concurrentlyinitializing the scan channels of internal logic circuits to be tested221 and boundary scan channels of the I/O circuits to be tested 222. Theboundary scan channels initialized in step 222 of FIG. 2 are theboundary scan receiver channels 132 and boundary scan driver channels134 of FIG. 1.

Continuing with the flow diagram 200 of FIG. 2, the boundary scanchannels are set up to accept input test data 223. For a boundary scandriver channel 134 (in FIG. 1), the input test data is provided byboundary test pattern generator 120 (FIG. 1). However, the input testdata for a boundary scan receiver channel 132 (in FIG. 1) is selectedfrom either data on an input pin of the integrated circuit or data frominternal test-pattern logic of the integrated circuit. During the systemclock phase of the LBIST, the internal logic of the integrated circuitis tested via the issuance of launch and capture clocks at the designedoperational speed of the chip. The LBIST circuit issues a launch clock(Clk-2) 224, which is input to boundary scan driver channels, toinitiate a low-clock-speed test of the I/O circuits. (Such alow-clock-speed test of the I/O circuits is also referred to as a DC I/Otest herein.) Boundary scan driver channels launch data stored in theboundary scan driver channels to output pins of the integrated circuit.Then system clocks (launch and capture), boundary scan receiver launchclocks, and boundary scan driver capture clocks, e.g., the clock signalsgenerated by on-product clock generators 160 a through 160 n in FIG. 1,are issued 225. The boundary scan receiver channels launch random datastored in boundary scan receiver channels via Clk-2, which issynchronously driven at machine speed with system launch clocks. Theboundary scan driver channels capture internal logic test results storedin boundary driver channels via Clk-1, which is synchronously driven atmachine speed with system capture clocks.

An iteration of the DC I/O test is completed with the issuance of an I/Oreceiver capture clock (CLK-1) 226. In response to a capture clockpulse, the boundary scan receiver channels store data from either anexternal input to the integrated circuit or internal test-pattern logic,i.e. boundary test pattern generator 120 in FIG. 1 via internal input136. The control processing for the logic built-in self-test continueswith decrementing an LBIST iteration count 227, which indicates thenumber of remaining LBIST iterations, and testing the current LBISTiteration count 228 to determine if further iterations are required. Ifthe LBIST iteration count is not equal to zero, another LBIST iterationis initiated by continuing the processing at the beginning of the LBISTcontrol loop, that is, setting up the boundary latches to accept inputfrom the scan path of the logic built-in self-test 220. Alternatively,if the LBIST iteration count is equal to zero, the LBIST mode is exited230.

The present invention utilizes a methodology which assures that a chip'sLBIST signature with the chip's I/O circuits uninhibited can bepredicted without knowledge of the configuration of the electronicpackage environment that will eventually accommodate the chip. Theboundary latch drive pattern is selected such that the same LBISTsignature is achieved when running standalone chip LBIST (I/O circuitsinhibited) or LBIST with I/O circuit verification (I/O circuitsuninhibited). With the signature made independent of the electronicpackage environment of the integrated circuit, various aggregations ofhardware with associated input/output connections can participate in alogic built-in self-test with integrated I/O circuit testing. To obtainan LBIST signature for an integrated circuit that is independent of theelectronic package environment, a deterministic data pattern is injectedinto the boundary driver latches during the scan phase of the LBIST. Oneexample of a universal deterministic driver data pattern for anyboundary scan chain, which is independent of inter-chip connections, isan alternating pattern of all zeros or all ones per LBIST cycle.

FIG. 3 illustrates one embodiment of deterministic boundary test patterngenerator 120 together with one embodiment of a boundary scan driverchannel 134, in accordance with an aspect of the present invention. Thisembodiment of boundary test pattern generator 120 comprises analternating pattern generator 314 and an enable signal generator 326.Alternating pattern generator 314 comprises latch 310 and logic inverter312. The output of latch 310 is coupled to an input of logic inverter312, and the output of logic inverter 312 is fed back to a data input oflatch 310. The output of alternating pattern generator 314 changes tothe logical inverse of the previous output of latch 310 when latch 310is clocked by a test system clock signal, resulting in an alternatingpattern of output data values. This alternating pattern of output datavalues from alternating pattern generator 314 is input to driver segment330 of boundary scan driver channel 134, which will be described furtherhereinbelow. The boundary test pattern generator may also provide inputdata for boundary scan receiver latches if the associated I/O pins arenot connected or non-deterministic by nature.

Enable signal generator 326 comprises an ID register 320, an ID_SELregister 322, and a comparator 324. The ID register stores anidentification number for an integrated circuit. The contents of theID_SEL register indicate the identification number of a targetintegrated circuit in the electronic package environment which iscurrently enabled to drive a shared data bus. Comparator 324 comparesthe current contents of ID register 320 to the current contents ofID_SEL register 322 and produces an enable signal which is input toenable segment 332 of boundary scan driver channel 134.

If the electronic package environment under test only containspoint-to-point I/O connections, then deterministic patterns are input toboundary scan driver channels to support I/O circuit testing within alogic built-in self-test of an integrated circuit. However, if theelectronic package environment under test contains shared buses orbi-directional buses, there is an additional requirement to support I/Ocircuit testing within a logic built-in self-test of an integratedcircuit. It is necessary to assure that only one chip which is coupledto a shared bus or bi-directional bus drives the shared orbi-directional bus at a time. This aspect of the technique for testingI/O circuits with an LBIST is referred to as orthogonal I/O drivecapability. Enable signal generator 326 of boundary test patterngenerator 120 and enable segment 332 of boundary scan driver channel 134comprise one embodiment of logic which provides orthogonal drivecapability.

FIG. 4 illustrates one embodiment of driver-boundary-latch enable-signallogic 400 for an electronic package environment having multiple packagelevels, in accordance with an aspect of the present invention. Theembodiment shown in FIG. 4 illustrates the combining of a chip enablesignal produced by enable signal generator 326 a and a card enablesignal produced by enable signal generator 326 b in AND-gate 430 toproduce a drive enable signal which is input to enable segment 332 ofboundary scan driver channel 134 in FIG. 3.

In order to provide orthogonal I/O drive capability for an electronicpackage environment with shared or bi-directional buses, an ID registeris also provided for each package level beyond the chip level. These IDregisters reside in each chip, and the ID register for each packagelevel must have a common size in all chips which participate in logicbuilt-in self-testing within the multiple-level electronic packageenvironment. The size of an ID register for a package level is chosen tobe commensurate with physical package requirements (e.g. the maximumnumber of chips on a card) plus an allowance for possible expansion.

It is advantageous for the ID register for the lowest package level tohave an odd number of bits. This assures that the LBIST iterations donot synchronize with the modulus (2) of the alternating pattern ofoutput data values from the alternating pattern generator, which drivesthe driver segment of a boundary scan driver channel. Consequently, thedriver segment of each boundary scan driver channel alternately receivesdata values of 0 and 1 for consecutive LBIST iterations. The ID registerfor each package level is defined to have one bit allocated for eachentity to be tested in that package level. For a card package level,each bit in the corresponding ID register would represent a chip. For aboard packaging level, each bit in the corresponding ID register wouldrepresent a card. The ID register hierarchy can be designed to apply tohigher package levels as well (e.g., a frame). The number ofpackage-level ID registers required is determined by how much of asystem's hardware is designed to participate in concurrent logicbuilt-in self-testing and I/O circuit testing. Although each registermust be designed to accommodate the maximum conceivable number of testentities, the number of bits required typically decreases for packagelevels which are higher in the electronic package environment hierarchy.That is, the number of chips is typically greater than the number ofcards, which is typically greater than the number of boards, forexample.

The contents of the ID_SEL register indicate the identification numberof a target integrated circuit which is currently enabled to drive ashared data bus in the electronic package environment. A dynamic,drive-selection register, i.e., an ID_SEL register, exists for eachdefined ID register, and a dynamic, drive-selection register is the samesize as the corresponding ID register. The dynamic, drive-selectionregisters for each package level are initialized with the same value;this initial value has only one bit on. The dynamic, drive-selectionregisters are ring shifted during each LBIST iteration. Thisinitialization and updating of the states of the dynamic,drive-selection registers results in drive orthogonality across the setof hardware under test by assuring that only the chip having the set ofID-register contents which matches the set of dynamic, drive-selectionregisters is allowed to drive a shared bus.

Although an integrated circuit may be prevented from driving a sharedbus for several LBIST iterations before the chip is allowed to drive theshared bus again, the chip will be enabled for many drive cycles duringI/O circuit testing with an LBIST because, typically, millions of LBISTiterations are required for coverage of a chip's internal logic. Also,it is possible to allow more than one chip to drive signal paths in theelectronic package environment concurrently if none of the outputcircuits of the enabled chips are coupled to the same signal path.Concurrent driving of signal paths in the electronic package environmentis effectuated by setting one or more of the same bit positions in thesame package-level ID registers in more than one chip to the enabledvalue. A concurrent drive configuration pattern for the ID registers canbe determined prior to testing integrated circuits of the electronicpackage environment based on knowledge of communication paths of theelectronic package environment (as illustrated later in the discussionof FIG. 6).

Referring again to FIG. 4, the illustrated embodiment ofdriver-boundary-latch enable-signal logic 400 comprises an enable signalgenerator for each level of the electronic package environment includedin the logic built-in self-test. As shown in FIG. 4, the enable signalgenerator for each level of the electronic package environment hasessentially the same structure. Chip-select enable signal generator 326a comprises chip ID register 320 a, chip ID_SEL register 322 a, and acomparator 324 a. Comparator 324 a comprises AND-gate logic 410 a, whichcomprises N two-bit AND gates and produces N corresponding AND-gateoutputs. The corresponding bits of chip ID register 320 a and chipID_SEL register 322 a are the input pairs to the N two-bit AND gates ofAND-gate logic 410 a. The N outputs of AND-gate logic 410 a are providedas the N inputs to an N-input OR gate 420 a, which produces achip-select enable signal.

Analogously, card-select enable signal generator 326 b comprises card IDregister 320 b, card ID_SEL register 322 b, and a comparator 324 b;comparator 324 b comprises AND-gate logic 410 b; and the N outputs ofAND-gate logic 410 b are provided as the N inputs to N-input OR gate 420b, which produces a card-select enable signal. For the example of FIG. 4in which the electronic package environment includes a chip level and acard level, the chip-select enable signal produced by chip-select enablesignal generator 326 a and the card-select enable signal produced bycard-select enable signal generator 326 b combined in AND gate 430 toproduce a drive enable signal for enable segment 332 of boundary scandriver channel 134 in FIG. 3.

As illustrated in FIG. 4, the dynamic, drive-selection registers, chipID_SEL register 322 a and card ID_SEL register 322 b, are ring shiftedso that the enable value, e.g. a bit value equal to 1, moves from onebit position of these ID_SEL registers to another adjacent bit positionwhen a shift is signaled. In addition, chip ID_SEL register 322 a andcard ID_SEL register 322 b are connected in a manner such that when abit value equal to 1 is shifted out of the least significant bit (LSB)of an ID_SEL register, a ring shift of the ID_SEL register correspondingto the next level of the electronic package environment is induced. Forexample, when the content of the LSB of chip ID_SEL register 322 a isequal to 1, a ring shift of card ID_SEL register 322 a also causes aring shift of card ID_SEL register 322 b in FIG. 4. A driver segment 330of boundary scan driver channel 134 in FIG. 3 is not enabled unless eachof bits in the chip's ID registers corresponding to a bit in the ID_SELregisters having a value of 1 also currently stores the value 1. Oneembodiment of logic for generating an enable signal in accordance withthis control rule from the contents of the ID registers and ID_SELregisters comprises comparator 324 a, comparator 324 b, and AND-gate 430as illustrated in FIG. 4.

U.S. patent application Ser. No. 10/753,852, filed Jan. 8, 2004, andpublished Jul. 14, 2005 as U.S. Patent Publication No. US 2005/0155003A1, by Rich et al., entitled “Scalable Logic Self-Test Configuration forMultiple Chips”, which is hereby incorporated herein by reference in itsentirety, discloses a method of synchronously self-testing hardwareconfigurations spanning multiple chips and multiple levels of anelectronic package environment. This method can advantageously utilizeintegrated logic built-in self-testing and testing of the input/outputcircuits of an integrated circuit in accordance with the presentinvention to verify an external signal path between chips of anelectronic package environment.

The present invention gives electronic hardware the capability tosimultaneously perform input/output connection checks and logic built-inself-testing of the internal logic circuits of an integrated circuit.Advantageously, the integration of these tests eliminates the need tomaintain input/output location and configuration data to supportboundary scan I/O testing. Also, the test overhead associated withconducting separate boundary scans during hardware power-on sequences iseliminated. Consequently, the time required to verify hardware atpower-on or reset is reduced. Moreover, if a failure is detected duringthe testing of an integrated circuit in an electronic packageenvironment, the techniques of the present invention also supporttraditional boundary scan testing to further isolate the failure.

This invention also provides a method of testing the I/O circuits ofdifferent integrated circuits which are connected to bi-directional orshared buses by arbitrating among the I/O circuits to prevent more thanone I/O circuit, which are connected to a bi-directional or shared bus,from simultaneously driving the bi-directional or shared bus duringtesting. The use of chip-resident ID registers and a dynamic,drive-selection registers provides distributed control to facilitatetesting multiple chips in multiple hardware package configurationswithout the need for maintaining chip configuration data. Furthermore,the present invention provides the capability to integrate I/Oconnection checks with logic built-in self-testing across multiplehardware package levels, e.g. from a chip on a card of a board toanother chip on another card of another board.

The present invention provides a simple-to-implement protocol thatsynchronizes multiple-chip LBIST executions, independent of theelectronic package configuration. This testing protocol assures that arepeatable and consistent signature is produced for each participatingchip which executes an LBIST, whether integrated I/O checking is enabledor disabled. This allows the mechanism of the present invention to beutilized in multiple-pass testing to diagnose I/O circuit problems. Forexample, the chips can proceed through logic built-in self-testing withI/O checking disabled (traditional LBIST). Then, the chips can be testedwith I/O checking enabled. By examining the LBIST signatures of twochips with and without I/O checking enabled, one can determine whetherthe location of the failure is a chip's I/O circuit, another circuit ofa chip, or an I/O signal path based on which signature is bad.

FIG. 5 illustrates an example of an electronic package environment 500in which integrated circuits perform logic built-in self-tests withintegrated input/output circuit testing, in accordance with an aspect ofthe present invention. Electronic package environment 500 comprises twoinstances of Chip 0 (chips 510 a and 510 d), two instances of Chip 1(chips 511 a and 511 d), chips 512 through 519, chip 560, four circuitcards (cards 520 a, 530, 540, and 520 d), and circuit board 550. Cards520 a and 520 d are of the same type, as indicated by their identicalpart numbers in FIG. 5.

Card 520 a comprises chip 510 a and chip 511 a, and chips 510 a and 511a communicate with each other, as illustrated in FIG. 5. Similarly, card520 d comprises chips 510 d and 511 d, which communicate with eachother. Card 530 comprises chips 512, 513, 514, and 515, which areinterconnected as shown in FIG. 5. Card 540 comprises chips 516, 517,518, 519, and 560, which are interconnected as shown in FIG. 5. Cards520 a, 530, 540, and 520 d each communicate with circuit board 550. Inthe example of FIG. 5, the hierarchy of the illustrated packaging levelsfrom lowest level to highest level is as follows: chip level, cardlevel, and board level.

The signal paths in the hardware configuration of electronic packageenvironment 500 of FIG. 5 include both bidirectional buses as well aspoint-to-point I/O paths between I/O circuits. Therefore, logic built-inself-testing of this electronic package environment requires that thechips be enabled to drive the signal paths orthogonally. To facilitatethe discussion of one embodiment of the control and coordination of thetesting of the chips' output circuits in accordance with the presentinvention, the I/O signal-path groups to and from each circuit card ofFIG. 5 are labeled with a circled number or the circled letter “B”. Thecircled number denotes the numeric part of the card name that aparticular card communicates with; that is, it indicates that the chipsof a given card communicate with the chips located on the designatedcard. The circled letter “B” denotes that the chips of a cardcommunicate with the circuit board I/O. For example, Card 1 520 a hastwo I/O groups, which communicate with Card 2 530 and the circuit boardI/O, respectively.

As discussed above, the registers used in generating the drive enablesignal are sized commensurate with the number of components in theelectronic package environment. The number of register bits for eachlevel of the electronic package environment must be greater than orequal to the number of components at each level, and it is advantageousto for the number of register bits to be an odd number for the firstlevel of the electronic package environment's hierarchy. In FIG. 5, thegreatest number of chips on a circuit card is five, and there are fourcircuit cards and only one circuit board. Therefore, the chip IDregister and the chip selection register (chip SEL_ID register) musthave at least five bits if design-specific optimizations are notconsidered. The card-level registers must have at least four bits.

FIG. 6 illustrates the identification register settings for twoexemplary test configurations of integrated circuits in the electronicpackage environment of FIG. 5, in accordance with an aspect of thepresent invention. In these examples, a common identification registerlength of five bits has been used for both package levels. The left sideof FIG. 6 illustrates one example of ID register settings which onlyenable one chip's boundary driver latches at a time for logic built-inself-testing of the integrated circuits in electronic packageenvironment 500 of FIG. 5. The right side of FIG. 6 shows one example ofoptimized ID register settings that take into account inherentlyorthogonal chips that can be enabled to drive their outputs at the sametime. Orthogonal (non-optimized) ID register settings are advantageousif the ID registers' contents are hardwired and other, unknown hardware,which participates in logic built-in self-testing, may be added later.

If the capability to load the ID registers at hardware initializationtime is provided, then one can take advantage of optimizations whichincrease the amount of time certain chips will be enabled to drive theiroutputs. Such optimizations allow inherently orthogonal chips tosimultaneously drive their outputs. Examples of inherently orthogonalchips are chips which do not communicate with one another, or the chipslocated on higher package-level components (e.g., cards) which do notcommunicate with one another. For example, in FIG. 5, Card 1 (520 a) andCard 4 (520 d) do not communicate with each other or with Card 3 (540).On Card 3 (540), Chip 7 (517) and Chip 8 (518) do not communicate withChip 9 (519) and Chip 10 (560). Also, there is an unused bit in theboard ID register because the board ID register has five bits, but thereare only four cards in the electronic package environment 500 of FIG. 5.

The right side of FIG. 6 illustrates optimizations that allow more thanone chip to drive their outputs concurrently. The chips of cards 520 aand 520 d are given the same bit designation in their board ID registersso that chips on these cards can be simultaneously drive enabled. OnCard 3 (540), chips 517 (Chip 7) and 518 (Chip 8) are given the samechip ID register bit assignments as chips 519 (Chip 9) and 560 (Chip10), respectively. Therefore, chips 517 and 519 (i.e., Chip 7 and Chip9) of card 540 (Card 3) will be enabled concurrently. Similarly, chips518 and 560 (i.e., Chip 8 and Chip 10) of card 540 (Card 3) will beenabled concurrently during time intervals when chips 517 and 519 arenot enabled. By assigning the value 1 to more than one bit in theidentification registers of the chips in an electronic packageenvironment, it is possible to repeat valid orthogonal drive-enableconfigurations to increase the output drive activity of the chips foreach cycle of the LBIST.

This illustrated by the contents of the ID registers of the chipscomprising card 540 (Card 3). Since there are only four circuit cards inthe electronic package environment of FIG. 5, the fifth bit of the boardID register is used to enable the chips of card 540 (Card 3) a secondtime during the logic built-in self-test cycle by assigning the value 1to the fifth bit of the board ID registers of all chips on card 540(Card 3). Also, because the number of bits in the card ID registersexceeds the number of chips on cards 520 a and 520 d (Card 1 and Card 4,respectively, in FIG. 6), the card ID registers of chips 510 a and 511 a(Chip 0 and Chip 1 of Card 1 in FIG. 6) and chips 510 d and 511 d (Chip0 and Chip 1 of Card 4 in FIG. 6) have more than one bit set equal to 1.In addition, chips 517, 518, 519, and 560 are enabled twice, asindicated by the two 1's in their card ID registers illustrated in FIG.6 under Card 3 and labeled Chip 7 card ID reg, Chip 8 card ID reg, Chip9 card ID reg, and Chip 10 card ID reg, respectively, each time thechips of card 540 are eligible to be enabled, which is indicated where abit value equal to 1 is placed in the chips' board ID registers.

In the example of FIG. 5, there are external inputs to the circuit boardof hardware configuration under test which are not driven according theboundary I/O requirements for a consistent signature. This are includedin board I/O groups 1 and 4, shown at top and bottom of FIG. 5,respectively. Consequently, the receiver boundary latches associatedwith board I/O of the chips on Card 1 (520 a) and Card 4 (520 d) must beconfigured to utilize their internal driver patterns when enteringself-test mode. The reason is that the chips of Card 1 (520 a) and Card4 (520 d) in FIG. 5 will receive these signals from the circuit boardI/O group B, which has an indeterminate input in this test environment.One embodiment of a receiver boundary latch, which facilitates thisselection of input signals for integrated LBIST and boundary I/Otesting, is disclosed below.

The boundary latch embodiments disclosed herein facilitate theintegration of I/O and LBIST testing. In accordance with an aspect ofthe present invention, a unique test mode is provided by receiverboundary latch embodiment which allows external inputs to the deviceunder test, i.e., an integrated circuit, to influence the state of theintegrated circuit's internal logic so that the final state of thechip's LBIST signature is a function of both the chip's internal logicand the data values input to the internal logic from the chip's externalinput pins during each cycle of an LBIST of the integrated circuit. Inaccordance with an aspect of the present invention, these boundary latchembodiments provide separate launch and capture latches, havingassociated launch and capture clock controls, in order to providecontrolled test sequences for testing the I/O pins of the integratedcircuit in LBIST mode. In these embodiments, all fundamental latches ofa boundary latch have a separate scan path, such that each fundamentallatch can be aggregated into an independent scan channel to be fed intoa multiple-input signature register (MISR) as shown in FIG. 1. Thisallows I/O test results to directly influence an LBIST signature.

A receiver boundary latch embodiment in accordance with the presentinvention provides a solution to the problem of the variability of thenature of the inputs provided to chip input pins by respect to externalinterfaces. In particular, some inputs to the integrated circuit may benon-deterministic due to the configuration or function of an electronicpackage environment. The receiver boundary latch embodiment of thepresent invention has the capability to select and utilize eitherexternal stimuli or internally generated stimuli during logic built-inself-test as indicated by control signals. This mechanism allows chipI/O, for a particular I/O group, to receive test stimuli concurrentlyfrom a source internal to the chip in order to maintain a predictablesignature value during concurrent testing of these chips.

Advantageously, these features are provided in a boundary latchembodiment which also supports use of the boundary latch to performtraditional LBIST or IEEE Standard 1149.1 Boundary Scan tests byproperly configuring them for such testing.

FIG. 7 illustrates one embodiment of a boundary receiver latch module700, in accordance with an aspect of the present invention. Boundaryreceiver latch module 700 comprises multiplexers 710, 720, 740, and 760and latches 730 and 750. The convention for all multiplexers illustratedin FIG. 7 is that a multiplexer selects the top input when the selectioninput of the multiplexer is a logic value equal to 0, and themultiplexer selects the bottom input when the selection input of themultiplexer is a logic value equal to 1. The following describes theoperation of boundary receiver latch module 700.

During normal operation of an integrated circuit, i.e., non-test mode,selection control inputs 784 and 787, Bscan_Rcv_Sel and Bscan_Drv_Sel,respectively, of multiplexers 710 and 760, respectively, are both setequal to 0 to enable a signal path comprising signal path segments 771,782, and 783 from an input pin to internal logic. In LBIST mode, latches730 and 750 must be initialized for each iteration of the self-test.This is accomplished by setting L1_Input_Sel input 785 and L2_Input_Selinput 786 equal to 1. These selection control input settings enableboundary scan path Bscan 1, comprising Prev_Bscan 1 input 774,multiplexer M2 output 775, and Next_Bscan 1 output 776, and boundaryscan path Bscan 2, comprising Prev_Bscan 2 input 778, multiplexer M3output 779, and Next_Bscan 2 output 780. Instances of boundary receiverlatch module 700 are appropriately connected to create one or moreboundary scan receiver channels 132, which feed an LBIST MISR, asillustrated in FIG. 1.

After latch initialization, latch 730 contains random launch data todrive internal logic of the integrated circuit. When the LBIST systemclocks are activated, clock signal CLK-2 789 is activated along with thechip's internal logic clocks in order to synchronously launch data fromlatch 730. L2_Input_Sel input 786 must be set to 0 and Bscan_Drv_Selinput 787 must be set to 1 to enable the path comprising latch L1 output777, multiplexer M3 output 779, latch L2 output 781, and multiplexer M4output 783 for data launch. A key feature of boundary receiver latchmodule 700 is the capability to capture external I/O values duringLBIST. External I/O values are captured during LBIST by setting theselection control inputs to the multiplexers as follows: Bscan_Rcv_Sel784 is set to 0; and L1_Input_Sel input 785 is set to 0. This allows anexternal input on an input pin to be captured by latch 730 when captureclock (CLK-1) 788 is activated via the path comprising signal pathsegments 771 and 773 and multiplexer M2 output 775. Alternatively, thereceiver boundary latch can be driven by an internally generated testpattern 772, which is input to multiplexer 710, if Bscan_Rcv_Sel 784 isset to 1. Then, the capture path on the activation of capture clock(CLK-1) 788 is internally generated test pattern 772, signal pathsegment 773, and multiplexer M2 output 775. The value of the selectioncontrol input for multiplexer 710, Bscan_Rcv_Sel 784, is determined as afunction of the topology of the electronic package environment and whichof the resulting I/O groups are to participate in the LBIST. Boundaryreceiver latch module 700 can also be utilized in standard boundary scantests by setting Bscan_Rcv_Sel 784 and L2_Input_Sel input 786 equal to0.

FIG. 8 illustrates one embodiment of a test input selection signalgenerator 800 for the input/output groups of an electronic packageenvironment, in accordance with an aspect of the present invention. Oneof the selection signals 840, 841, 842, 843, through 844 is provided asthe selection control input, Bscan_Rcv_Sel 784, to multiplexer 710 inFIG. 7. Test input selection signal generator 800 of FIG. 8 comprisesI/O group fence register 820 and AND-gates 831, 832, 833, though 834.Self-test-mode signal 810 is provided as an input to test inputselection signal generator 800. Self-test-mode signal 810 indicateswhether the chip is currently in a self-test mode or non-test mode ofoperation. I/O group fence register 820 comprises n bits, one bit foreach of n possible I/O groups. The bits stored in I/O group fenceregister 820 indicate whether corresponding receiver boundary latchesare to receive test inputs from external inputs to the integratedcircuit or an internal test pattern generator during LBIST.Self-test-mode signal 810 is passed along as selection signal SEL0 840.On the other hand, selection signals SEL1 841 through SELn 844 areprovided by the outputs of AND-gates 831 through 834. Selection signals841, 842, 843, and 844 are computed as the logical-AND function ofself-test-mode signal 810 and fence register bits 821, 822, 823, and824, respectively.

If a chip I/O group is to always utilize an internally generated testpattern for logic built-in self-testing, selection signal SEL0 840 isprovided as the selection control input, Bscan_Rcv_Sel 784, tomultiplexer 710 of each instance of the boundary receiver latch modulein FIG. 7 for the chip I/O group. A chip I/O group must utilize aninternally generated test pattern for LBIST in the following situation,for example: the chip I/O group may receive input from circuitry thatdoes not control its output circuits according to the requirements forintegrated testing of I/O circuits and LBIST. In this situation, theselection of input signals for the effected I/O group is notconfigurable in self-test mode. For configurable LBIST cases, the I/Ofence register is used to select which I/O groups will receive externalinput and which I/O groups will receive internally generated datapatterns. In other words, the bit values stored in I/O group fenceregister 820 either allow receiver boundary latches of an I/O group toreceive external inputs during LBIST or isolate receiver boundarylatches of an I/O group from the inputs of non-participating interfacesby driving the I/O group with an internally generated pattern. ThisLBIST configurability can be used for diagnostic purposes or to supportmultiple hardware configurations.

FIG. 9 illustrates one embodiment of a boundary driver latch module 900,in accordance with an aspect of the present invention. Boundary driverlatch module 900 comprises three multiplexers (910, 930, and 950) andtwo latches (920 and 940). The convention for all multiplexersillustrated in FIG. 9 is that a multiplexer selects the top input whenthe selection input of the multiplexer is a logic value equal to 0, andthe multiplexer selects the bottom input when the selection input of themultiplexer is a logic value equal to 1. The following describes theoperation of boundary driver latch module 900.

During normal (non-test mode) operation, the Bscan_Drv selection signal975 is set equal to 0 to enable a direct path from internal logic input961 to output 972 via path segment 971. In LBIST mode, latch 920 andlatch 940 must be initialized for each iteration of the self-test. Thescan path of latch 920 (Bscan 1) is enabled by setting the selectionsignal L1_Input_Sel 973 equal to 1. The scan path of latch 920 comprisesPrev_Bscan1 input 963, multiplexer M1 output 964, and Next_Bscan1 output965. Similarly, the scan path of latch 940 (Bscan 2) is enabled bysetting the selection signal L2_Input_Sel 974 equal to 1. The scan pathof latch 920 comprises Prev_Bscan2 input 967, multiplexer M2 output 968,and Next_Bscan2 output 969. The previous and next boundary scan inputsand outputs are appropriately connected to other boundary driver latchmodules to create driver boundary scan channels which can feed an LBISTMISR as illustrated in FIG. 1. After latch initialization, the latch 920contains datum of a deterministic data pattern to drive an external I/Oconnection during the launch phase of boundary driver latch operationfor LBIST. Clock signal CLK-2 977 is activated to synchronously launchdata from latch 920. Selection signals L2_Input_Sel 974 andBscan_Drv_Sel 975 must be set to 0 and 1, respectively, to enable thesignal path for data launch, i.e., from latch L1 output 966 tomultiplexer M2 output 968 to latch L2 output 970 to output 972. Datumfrom internal logic that drives I/O pins is captured when capture clock(CLK-1) 976 is activated along with internal logic capture clocks.Selection signal L1_Input_Sel 973 is set to 0 to enable the data capturepath from internal logic input 961 to multiplexer M1 output 964 (viamultiplexer M1 input 962) on capture clock (CLK-1) 976 activation.Alternatively, a traditional boundary scan test, in which there is noscan channel for latch 940, can be conducted by setting selection signalL2_Input_Sel 974 equal to 0.

FIG. 10 illustrates one embodiment of a boundary driver latch module1000 for a bi-directional driver or bus, in accordance with an aspect ofthe present invention. Boundary driver latch module 1000 for abi-directional bus comprises Bscan driver latch enable circuit 1001,boundary driver latch module 900 for data, and tri-state device 1080.Bscan driver latch enable circuit 1001 controls which direction data isflowing through I/O pin 1081, which is connected to a bi-directionaldriver or bus. When control input 1072 to tri-state device 1080 is setequal to 1, tri-state device 1080 enters a high impedance state thateffectively disconnects boundary driver latch module 900, which drivesdata input 1073 of tri-state device 1080. This allows path 1082 tofunction as an input connection from I/O pin 1081. When I/O pin 1081 isconnected to a bi-directional driver or shared bus, another chip candrive data onto the bi-directional driver or common bus when tri-statedevice 1080 of boundary driver latch module 1000 is in a high impedancestate.

The structure of Bscan driver latch enable circuit 1001 is essentiallythe same as the structure of boundary driver latch module 900, which isillustrated in FIG. 9. As illustrated in FIG. 10, Bscan driver latchenable circuit 1001 comprises multiplexers 1010, 1030, and 1050 andlatches 1020 and 1040.

Bscan driver latch enable circuit 1001 provides control input 1072 totri-state device 1080. At latch initialization time of each LBISTsequence, latches 1020 and 1040 can be initialized with initializationvalues from their respective scan paths when selection inputsL4_Input_Sel 1073 and L5_Input_Sel 1074 are set to 1. This enables thescan path (Bscan 3) of latch 1020, which comprises Prev_Bscan3 input1063, multiplexer M4 output 1064, and Next_Bscan3 output 1065, and thescan path (Bscan4) of latch 1040, which comprises Prev_Bscan4 input1067, multiplexer M5 output 1068, and Next_Bscan4 output 1069. Thecapability to initialize latches 1020 and 1040 for each LBIST iterationprovides the capability to select one boundary driver latch module ofmultiple boundary driver latch modules in an electronic packageenvironment to drive a bi-directional bus or shared bus for each LBISTiteration. When an integrated circuit operates in LBIST mode, thelatches of boundary driver latch module 900 of boundary driver latchmodule 1000 for a bi-directional driver or bus must also be initializedfor each LBIST iteration as described above in conjunction with FIG. 9.

By setting selection signals L2_Input_Sel 974 (FIG. 9) and L5_Input_Sel1074 (FIG. 10) equal to 0, boundary driver latch module 1000 forbi-directional and shared buses can be utilized in traditional boundaryscan tests.

The boundary latch embodiments of the present invention provide thefollowing unique features that enable electronic hardware toconcurrently perform input/output connection checks and LBIST of achip's internal logic: a capability to configure boundary driver latchoperation such that external input values influence an LBIST signature;separately controlled launch and capture paths within a boundary latch;a capability to include all latches of a boundary latch in scan channelsfor LBIST; a capability to control which I/O groups participate inLBIST; control of data flow on bi-directional and shared buses eachLBIST iteration; and configuration controls which support traditionalboundary scan testing as well as new test modes.

The capabilities of one or more aspects of the present invention can beimplemented in software, firmware, hardware or some combination thereof.

One or more aspects of the present invention can be included in anarticle of manufacture (e.g., one or more computer program products)having, for instance, computer usable media. The media has therein, forinstance, computer readable program code means or logic (e.g.,instructions, code, commands, etc.) to provide and facilitate thecapabilities of the present invention. The article of manufacture can beincluded as a part of a computer system or sold separately.

Additionally, at least one program storage device readable by a machineembodying at least one program of instructions executable by the machineto perform the capabilities of the present invention can be provided.

The flow diagrams depicted herein are just examples. There may be manyvariations to these diagrams or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order, or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the following claims.

1. A method comprising: verifying at least one external signal path ofan electronic package environment by concurrently testing aninput/output (I/O) circuit of an integrated circuit of the electronicpackage environment while testing the integrated circuit using a logicbuilt-in self test (LBIST) of the integrated circuit, the at least oneexternal signal path being electrically coupled to the I/O circuit, andthe concurrently testing producing a signature test result of theintegrated circuit; and wherein the signature test result furthercharacterizes a response of the I/O circuit to the LBIST, and theverifying the at least one external signal path employs the signaturetest result produced using the LBIST.
 2. The method of claim 1, whereinthe verifying further comprises concurrently testing at least anotherI/O circuit of at least another integrated circuit of the electronicpackage environment using at least another LBIST of the anotherintegrated circuit, the at least another I/O circuit being electricallycoupled to the at least one external signal path.
 3. The method of claim2, wherein the I/O circuit of the integrated circuit provides a testinput to the at least another I/O circuit of the at least anotherintegrated circuit via the at least one external signal path.
 4. Themethod of claim 1, further comprising concurrently testing at least oneother circuit of the integrated circuit using the LBIST.
 5. The methodof claim 1, wherein a test input for the I/O circuit is selected from anexternal input to the integrated circuit on the at least one externalsignal path or a test pattern generated by the LBIST of the integratedcircuit.
 6. The method of claim 5, wherein the test input comprisesdeterministic test data generated by the LBIST.
 7. The method of claim1, further comprising concurrently verifying at least another externalsignal path of the electronic package environment by concurrentlytesting at least another I/O circuit of at least another integratedcircuit of the electronic package environment using at least anotherLBIST of the another integrated circuit, the at least another externalsignal path being electrically coupled to the at least another I/Ocircuit.
 8. The method of claim 1, further comprising: verifying atleast another external signal path of the electronic package environmentby testing at least another I/O circuit of the integrated circuit usingthe LBIST, the at least another external signal path being coupled tothe at least another I/O circuit; and wherein the signature test resultof the integrated circuit characterizes a response of the at leastanother I/O circuit to the LBIST.
 9. A system comprising: a logicbuilt-in self test (LBIST) for an integrated circuit of an electronicpackage environment; and means for verifying at least one externalsignal path of the electronic package environment by concurrentlytesting an input/output (I/O) circuit of the integrated circuit whiletesting the integrated circuit using the LBIST of the integratedcircuit, the at least one external signal path being electricallycoupled to the I/O circuit, and the concurrently testing producing asignature test result of the integrated circuit, wherein the signaturetest result further characterizes a response of the I/O circuit to theLBIST, and the verifying at least one external signal path employs thesignature test result produced using the LBIST.
 10. The system of claim9, wherein the means for verifying further comprises means forconcurrently testing at least another I/O circuit of at least anotherintegrated circuit of the electronic package environment using at leastanother LBIST of the another integrated circuit, the at least anotherI/O circuit being electrically coupled to the at least one externalsignal path.
 11. The system of claim 10, wherein the I/O circuit of theintegrated circuit provides a test input to the at least another I/Ocircuit of the at least another integrated circuit via the at least oneexternal signal path.
 12. The system of claim 9, further comprisingmeans for concurrently testing at least one other circuit of theintegrated circuit with the LBIST.
 13. The system of claim 9, wherein atest input for the I/O circuit is selected from an external input to theintegrated circuit on the at least one external signal path or a testpattern generated by the LBIST of the integrated circuit.
 14. The systemof claim 13, wherein the test input comprises deterministic test datagenerated by the LBIST.
 15. The system of claim 9, further comprisingmeans for concurrently verifying at least another external signal pathof the electronic package environment by concurrently testing at leastanother I/O circuit of at least another integrated circuit of theelectronic package environment using at least another LBIST of theanother integrated circuit, the at least another external signal pathbeing electrically coupled to the at least another I/O circuit.
 16. Atleast one program storage device readable by a machine embodying atleast one program of instructions executable by the machine to perform atesting method, the method comprising: verifying at least one externalsignal path of an electronic package environment by concurrently testingan input/output (I/O) circuit of an integrated circuit of the electronicpackage environment while testing the integrated circuit using a logicbuilt-in self test (LBIST) of the integrated circuit, the at least oneexternal signal path being electrically coupled to the I/O circuit, andthe concurrently testing producing a signature test result of theintegrated circuit; and wherein the signature test result furthercharacterizes a response of the I/O circuit to the LBIST, and theverifying the at least one external signal path employs the signaturetest result produced using the LBIST.